Refactor compute manager _get_instances_by_driver

Make the method more efficient by only querying nova-conductor
once. Also limit fallback instance query to host only. This is
in preparation for fixing bug 1129519.

Change-Id: I7de14f1ffda37c14f760f602fd81250d2163b430
Make ComputeManager _running_deleted_instances query by uuid

Reuse existing _get_instances_on_driver method to query driver for
running instances.

Resolves bug 1129519.

Change-Id: I9186b289fadfc4414874b3ba52195e9acfac18b4